Impact of Topology on the Characteristics of Water inside Cubic Lyotropic Liquid Crystalline Systems

Abstract

Water molecules present inside the lipid-based cubic liquid crystalline phases are found to play a major role in wide range of applications, such as protein crystallization, virus detection, delivery of drug and biomolecules, etc. In this regard, it is crucial to elucidate static and dynamic properties of the water molecules in the nanochannels and to explore the effect of geometrical topology on the nature of the water inside the different cubic phases. In the present work, we have incorporated two probes, coumarin-343 (C-343) and coumarin-480 (C-480), in two cubic phases with different symmetries, namely gyroid (Ia3d) and double diamond (Pn3m) with the same water content (22%), to probe the micropolarity, the microviscosity, and the hydration dynamics at different hydrophobic depths in the mesophases. Steady state results estimate the polarity at the lipid–water interface to be similar to that of ethanol, and the polarity near the more hydrophilic parts of the nanochannel resembles that of ethylene glycol. We have also observed a gradient in the microviscosity inside the LLC nanochannels from time-resolved fluorescence anisotropy studies. The hydration dynamics, which play a key role in the numerous applications of the mesophases, have been probed by the time-dependent Stokes shift method of the two probes, revealing the existence of three kinds of dynamics. The difference in the hydration dynamics inside the two mesophases, where the water molecules confined in the Ia3d phase exhibit a slower dynamics compared to that in Pn3m, is the prime importance of this work. The underlying reason for this disparity is majorly associated with the differences in the topology of the two structures including the hydrophobic packing stress, the negative interfacial curvature, and the curvature elastic energy of the lipid–water interface. We believe that this kind of correlation between the structural topology of the different cubic LLC mesophases and nature of the water nanochannel will help to boost the applications of the cubic phases in the future.